Regents Biology

The Chemical Basis of Life

Sections 2.6 – 2.9Chemical Bonding

Today we will learnabout how atoms

bond together

Regents Biology

Review Atomic Strucutre

Regents Biology

Chemical Bonding Properties Bonds are made with

electrons electrons determine

chemical “behavior” of atom

depends on numberof electrons in atom’s outermost shell valence electrons

How many valenceelectrons do you see?

How many valenceelectrons do you see?

Regents Biology

Elements & their valence shells

Elements in the same row have the same number of shellsElements in the same row have the same number of shells

Moving from left to right, each element has a sequential addition of electrons (& protons)Moving from left to right, each element has a sequential addition of electrons (& protons)

Regents Biology

Elements & their valence shells

Elements in the same column have the same valence & similar chemical properties

Elements in the same column have the same valence & similar chemical properties

Regents Biology

Bonding Properties

Effect of electrons Atoms like to have maximum number of

valence electrons!!!!!

What’s themagic number?

How does this atom behave?How does this atom behave? How does this atom behave?How does this atom behave?

Regents Biology

–

–

–

Chemical Reactivity So atoms tend to complete a partially

filled valence shell or empty a partially filled valence shell

This tendency drives chemical reactions…This tendency drives chemical reactions…

and creates bondsand creates bonds

Regents Biology

Chemical Reactivity Quiz

Regents Biology

–

–

H2 (hydrogen gas)

Covalent bond

Bonds in Biology Ionic Bonds (atoms to ions) Covalent Bonds (shares e-)

nonpolar & polar

Hydrogen Bonds

Hydrogen bond

H2O

H2O

Ionic bond

Regents Biology

LE 2-7a-1

Transfer ofelectron

NaSodium atom

ClChlorine atom

Ionic Bonds

Ion – any atom that has lost or gained an electron.

Regents Biology

LE 2-7a-2

Na

Sodium ionCl

Chloride ion

Sodium chloride (NaCl)

Ionic Bonds

Regents Biology

Na

Cl

Regents Biology

Covalent bonds Covalent bonds are strong bonds

two atoms share a pair of electrons both atoms holding onto the electrons very stable

Forms molecules

–

–

H2 (hydrogen gas)H2 (hydrogen gas)

H — HH2O (water)H2O (water)

H

H

Oxygen

H

HO

Regents Biology

Multiple covalent bonds 2 atoms can share >1 pair of electrons

double bonds 2 pairs of electrons

triple bonds 3 pairs of electrons

Very strong bonds

H

H–C–H

H

––

More isbetter!

Regents Biology

Nonpolar covalent bonds Pair of electrons shared equally by 2 atoms

example: methane (CH4 )

H

H–C–H

H

––

Regents Biology

H

H

Oxygen

Polar covalent bonds

Pair of electrons shared unequally by 2 atoms example: water = H2O

oxygen has stronger “attraction” for the electrons than hydrogen

water is a polar molecule

+

+

––

––

Regents Biology

Covalent Bond

A water molecule

Regents Biology

Penguins gone bad!

AnyQuestions?